This invention relates in general to a sewing machine for producing a stitch contour in a workpiece according to a predetermined program. A movably arranged workpiece receiving device is controlled with respect to the needle by means of a linkage cooperating with a control cam. In particular, a new device mounts adjustably the control cam to affect portions of the stitch contour with respect to their relative position.
Generally it is known to adjustably mount the control cam of a sewing machine of the aforementioned type, in order to synchronize the feed movement of the workpiece receiving device in relation to the stitch forming elements.
In U.S. Pat. No. 2,495,069 there is illustrated such a sewing machine, in which the control cam is mounted by a device to allow an angular adjustment. From U.S. Pat. No. 2,410,679 there is known a hub connection provided with a device to allow an angular fine adjustment, in which a hub may be adjusted in relation to a shaft by set screws.
Moreover, in U.S. Pat. No. 4,073,252 there is illustrated a sewing machine of the kind described above, for stitching a pocket to a workpiece. In contrast to the aforesaid sewing machines there are produced here stitch contours of a relative large size and which are fixed in their geometric configuration. Due to the limitation of the size of the control cam, such large stitch contours are essentially achieved by applying a linkage installed with a large ratio for converting the drive movements of the cam to the required movements of the workpiece holder, according to the stitch configuration in relation to the needle. As further described, the clamping plate moves the workpiece including the pocket on a stationary base plate by which forces of friction are induced into the control system depending on the material of the workpiece. Furthermore, a shifting at the workpiece and within the layers is caused by the continuous workpiece feeding movements regardless of the needle penetrating the material. Due to these circumstances, the geometry of the stitch configuration is negatively affected. Considering additionally the facts, that the linkage shows a different mechanical stiffness depending on the direction of the feed, it becomes quite obvious, that such influences cannot be taken in account when determining the cam data.
In the process of attaching a pocket to a workpiece by means of a double U-shaped stitch pattern, the aforesaid described problem of geometric deformation causes unequal distances between the individual stitch portions, and injures the appearance of the work. This is most important, if the stitch pattern is emphasized by using a specially colored thread for decorative purposes.
In practice, it has been shown that an exactly computed control cam of such type of sewing machine, does not necessarily furnish the desired quality with respect to the geometric configuration of a sewn pattern at the first attempt. Since there are no possibilities of adjustment, a corrected control cam must be consequently produced in order to compensate the above-described influences. Such an experimental method for producing the control cam is time-consuming and expensive. It is furthermore connected with significant problems when providing a sewing machine already in the field, with another control cam in order to produce a different stitch pattern, as the described influences depending on the material to be processed and the geometry of the stitch pattern, may be judged only after the sewing process.
Accordingly, it is the main object of the present invention to install in a cam controlled linkage of a sewing machine an adjustment device which makes it possible to adjust portions of the stitch pattern in their geometric arrangement.
It is a further object of the present invention to eliminate the experimental procedure of producing a control cam in order to reduce time and costs.
A still further object of the present invention is to create an adjustment device which makes it possible to supply control cams for producing different stitch patterns with sewing machines that are already in the field.
Another object of the present invention is to make the adjustment device of the aforesaid character a part of the sewing machine, so as not to increase the costs of the pattern-depending control cam.
Still another object of the present invention is to provide a device of the aforegoing character which is simple in construction and reliable in operation.